The 500-KW CW X-band Goldstone System Radar

Abstract

In recent years the Goldstone Solar System Radar (GSSR) has undergone significant improvements in performance in the areas of increased transmitter power and increased receiver sensitivity. An overview is presented of the radar system and each of these improvements is discussed. Additional plans for future improvements are also described Introduction The Goldstone X-Band (8.51-GHz) Continuous-Wave Solar System Radar (GSSR) is one of the few radar instruments in the world used to study the Solar System. Many observations have been conducted of the planets Mercury, Venus, and Mars, its moon Phobos, the Galilean satellites of Jupiter, the rings of Saturn and its moon Titan, as well as near-Earth asteroids and comets. The Goldstone Solar System Radar is a part of NASA’s Deep Space Network of antennas, which provides 24-hour-a-day communication for unmanned space exploration projects. The network consists of three complexes around the world, one near Madrid, Spain, one near Canberra, Australia, and one in the Mojave Desert at Goldstone, California. The GSSR is installed on the Goldstone 70m Cassegrain antenna (Figure 1). In addition to its primary purpose of tracking spacecraft, the 70m antenna is also used for radio astronomy at L-, S-, Xand Ka-band frequencies and radar astronomy at S and X-band. The 70m antenna is a shaped reflector system featuring an asymmetric subreflecfor that can focus on any of the many feeds at the center of the main reflector (see Figure 1). The focus is changed from one feed to another by rotating the subreflector about its mechanical axis. The operation of the radar requires the subreflector to be moved between the transmit and receiver feeds when switching between the transmit and receive portions of the radar cycle. This movement takes approximately 30 seconds and prohibits observations of near-Earth targets where the round-trip lighttime is short. Recent changes in two elements of the radar have improved its performance by 2.0 dB. The transmitter was upgraded with two new state-of-the-art 250-kW X-bandl klystrons, which increased the radiated power from 360 kW to 460 kW (1.1 dB). The microwave receive system was improved by cryogenically cooling a major portion of the receive feed components, reducing the receiver noise temperature from 18.0 K to 14.7 K (0.9 dB).